This invention relates to circuitry for separating chrominance and luminance components from composite video signal, and more particularly to a comb filter utilizing a one field delay and incorporating circuitry to compensate for motion induced artifacts.
The use of comb filters for separating luminance and chrominance is well known by those skilled in the art of video processing. Hardware cost restraints, however, have generally limited their implementation to relatively simple interline comb filters (a description of an interline comb filter may be found in RCA Review, Vol. 41, No. 1, March 1980, pp. 3-28, in the article by D. H. Pritchard, entitled "A CCD Comb Filger for Color TV Receiver Picture Enhancement", which is incorporated herein by reference).
Interline comb filters effectively separate chrominance and luminance components but produce several undesirable effects. These effects include: loss of diagonal resolution; reduction of vertical resolution; and the production of "hanging dots" along vertical transitions.
Interframe comb filters which operate on signals separated by integral video frame intervals separate chrominance and luminance components without any of the foregoing undesirable effects. However, interframe comb filters generate extremely annoying artifacts around the edges of moving image objects. To overcome this shortcomming it has been proposed to utilize adaptive comb filters. One such adaptive filter combines a line comb filter with a frame comb filter. In this arrangement, separated luminance and chrominance is acquired from the line comb filter during intervals of interimage motion and from the frame comb filter in the absence of motion. Adaptive systems, though producing generally improved signals, are costly to realize and have compromised performance.
The present invention is a comb filter system which is generally superior to the interline comb filter or the adaptive interframe comb filter but requires significantly less hardware than the interframe comb filter.